Precipitation Hardening Heat Treatment Research Articles

Binder Based Processing of Magnesium Alloy WE43 towards Biomedical Application Using Metal Injection Molding (MIM)

In this study to the authors knowledge 1st time, Metal Injection Molding (MIM) technique was used to introduce the magnesium alloy WE43 into binder-based powder metallurgical (PM) processing. Towards later adoption to binder-based 3D-printing technologies, Fused Granular Fabrication (FGF) technique, respectively for biomedical application. Metal Injection Moulding (MIM) is a binder based economic near net shape prototyping technique for production of complex shaped parts in high number and high reproducibility, and hence perfect as a “gold standard” for the introduction of new Mg-alloys into binder passed PM processing. In doing so, dogbone shape tensile test specimen were manufactured by MIM, subsequently solvent debound and conventional sintered in argon atmosphere. Next to the as sintered specimens (asS), solid solution heat treatment (T4) and precipitation hardening heat treatment (T6) were performed on additional specimens. Tensile tests pointed out high strength and ductility of as sintered and heat treaded specimens of up to 226 MPa UTS at 7.6% elongation at fracture. The microstructure was investigated using SEM imaging technique equipped with energy disperse x-ray energy analysis (EDX) for secondary phase analysis. Hence, the magnesium alloy WE43 could be identified as a high strength and ductility alloy for binder based PM processing for future additive manufacturing approaches in biomedical applications of patient adapted implants.

Investigation of microstructural, mechanical and tribological properties of Al356/3-9%ZrB2 composites produced by the stir casting process

In this study, aluminum 356 cast alloy as the metal matrix was strengthened with various amounts (3, 6 and 9 weight percent) of ZrB2 reinforcement particles via stir casting process. The reinforcement particles were injected into the melt during the casting. Furthermore, precipitation hardening (T6) heat treatment was carried out on a series of the cast samples. Morphology and microstructure of the samples were studied by scanning electron microscopy (SEM), while elemental and phase analyses were conducted by EDS and XRD. Investigation of mechanical properties (wear resistance, tensile strength and micro-hardness) showed considerable improvement with increased content of the reinforcement material. In this regard, the tensile strength increases from 135 MPa in the matrix material to 248 MPa in the composite sample which contained 9% ZrB2. Furthermore, after a sliding distance of 2000 m in wear tests, the weight loss of the same two samples were 0.0604 and 0.0218 g, respectively. In this regard, T6 heat treatment significantly improved the mechanical and tribological properties of the composite such that an increase of ∼30% in tensile strength and a decrease of more than 60% in wear weight loss were achieved in the specimen with 9% ZrB2.

Phase transformation dynamics guided alloy development for additive manufacturing

Fusion-based additive manufacturing technologies enable the fabrication of geometrically and compositionally complex parts unachievable by conventional manufacturing methods. However, the non-uniform and far-from-equilibrium heating/cooling conditions pose a significant challenge to consistently obtaining desirable phases in the as-printed parts. Here we report a martensite stainless steel development guided by phase transformation dynamics revealed by in-situ high-speed, high-energy, high-resolution X-ray diffraction. This developed stainless steel consistently forms desired fully martensitic structure across a wide range of cooling rates (102–107 ℃/s), which enables direct printing of parts with fully martensitic structure. The as-printed material exhibits a yield strength of 1157 ± 23 MPa, comparable to its wrought counterpart after precipitation-hardening heat-treatment. The as-printed property is attributed to the fully martensitic structure and the fine precipitates formed during the intrinsic heat treatment in additive manufacturing. The phase transformation dynamics guided alloy development strategy demonstrated here opens the path for developing reliable, high-performance alloys specific for additive manufacturing.

Effect of thixoforming and precipitation hardening on microstructure and mechanical properties of Al-10.5Si–3Cu-0.2Mg alloy produced by strain induced melt activation process

The effects of the thixoforming and the precipitation hardening heat treatment on the microstructure and mechanical properties of Al-10.5Si–3Cu-0.2Mg alloy produced by the strain-induced melt activation (SIMA) process have been investigated. According to previous researches of authors, new introduced alloy has superior mechanical properties in addition to good response to aging process compared with the casting aluminum alloys. The results of the image analysis showed that by increasing the deformation from 10% to 20% and the time of semi-solid heat treatment from 10 to 20 min, the best globular structure of α(Al) grains with the grain size and shape factor of 65 μm and 0.81 were obtained at 15 min for 20% pre-deformation, respectively. The thixoforming process increased the ultimate tensile strength of the alloy about 29%, the yield strength about 37% and the elongation about 6%, compared to the as cast condition. The 20% pre-deformed sample experienced precipitation hardening heat treatment in addition to thixoforming had the best mechanical properties having UTS, YS, elongation and hardness of 423 MPa, 331 MPa, 4.41%, and 144.24 BHN, respectively. Thixoforming plus precipitation hardening is an effective procedure to produce a particular microstructure in Al–Si–Cu–Mg system exhibiting the excellent castability and high mechanical properties.

The Effect of Precipitation hardening Heat Treatment on Impact Toughness and Tensile Properties of AA6063 Aluminum Alloy Reinforced with Hybrid Particles from Al2O3 and Graphite

Aluminum based composite are getting a vast scope nowadays because of its high properties and availability as fit large industrial development. (AMC) Aluminum metal-matrix composites is new engineering materials which contains two or more materials with different properties one being a metal from Aluminum and other may be metal, ceramic , glass reinforced materials. So in This present article We try to prepare hybrid composite materials based on aluminum alloy (AA6063) and reinforcement it by shared particles having size of micron of Alumina (7.5 wt%) and Graphite particles are added in specific countrified parentage (2.5 , 5 , 7.5 , 10 wt%) by stir casting technique to obtain hybrid Aluminum Which having the improving mechanical properties ,Heat treatment (solution heat treatment-artificial aging) are carried out on all samples ,After that inspections and mechanical tests have be done on all reinforcement samples , The results of Scanning electron microscope have shown uniform distribution of hybrid reinforced particles in matrix alloy and hybrid reinforced Aluminum alloy successfully prepared using stir casting method. The results of tests have shown The Impact toughness, , and Ultimate tensile strength were determined, with the addition of reinforcement the properties and effect of Precipitation hardening Heat treatment are improved compared to the parent metal Aluminum (6063) alone.

Investigation and analysis of aging behavior and tensile fracture study on precipitation hardened al7075-white cast iron particulate reinforced composites

In this research work the machining waste white cast iron powder (WCI) is introduced in the age hardenable Al7075 alloy matrix with the objective of enhancing the tensile properties by well-known age hardening treatment. This material holds good in light duty dies where in the strength-related characteristics improvement is the order of the day. In view of this the effect of aging kinetics on the hardness pattern and tensile strength of stir cast Al7075-white cast iron (WCI) particulate reinforced composites in as cast and peak aging conditions is investigated. The composite is cast by two step liquid stir casting route. During precipitation hardening heat treatment, reinforcement weight percentage (internal variable) and aging temperature (external variable) are considered to be the major strengthening variables. To understand the nature of failure in tensile study, fracture surface analysis is carried out using SEM. The experimental values revealed that there is a substantial enhancement in the desired properties during the precipitation hardening treatment, if the strengthening variables are properly controlled. Hardness and tensile strength of the composite have increased with increase in weight percentage of reinforcement and reduction in aging temperature. Maximum hardness and tensile strength are observed when Al7075 alloy is reinforced with 6 weight% of WCI, aged at 100ᴼC. SEM images of tensile fracture surface exhibits abundant cup-like depressions or dimples as well as river patterns indicating mixed mode of failure. The equally aligned facets (dendrites) present in the peak-aged fracture surfaces is the evidence for the attainment of optimum (peak) aging condition. The aim of the present research work is to improve the hardness-related properties by the combined effect of precipitation of secondary phases (intermetallics) through aging treatment and dispersion strengthening by the introduction of hard reinforcement WCI.

Wear behavior of Ni-B coated-hard anodized Al7Si alloy and machining performance with ZrN ceramic film coated carbide tool

In this study, it is aimed to increase the wear resistance of Al7Si alloy, which is widely used in the manufacturing industry, with different surface treatments and to propose an effective and economical cutting tool coating for machining process of the alloy. Accordingly, precipitation hardening heat treatment, Hard Anodizing and Ni-B coating processes were applied to cast Al7Si alloy samples. The structural, mechanical and tribological properties of the samples were characterized after the surface treatments. Also, the machining performance of Al7Si alloy with uncoated and ZrN ceramic film coated carbide end mills was investigated. The milling processes were performed to determine the actual working performance of the tools. SolidCAM i-machining module, which has become widespread recently, was used as intelligent machining instead of the tool paths used in traditional methods. After the precipitation hardening heat treatment, Hard Anodizing and Ni-B coating process were applied to the alloy, the wear volumes were greatly reduced. The lowest wear volume was obtained for the Ni-B coated Al7Si alloy, which also achieved the lowest coefficient of friction. After machining studies, it was determined that the ZrN coating reduced the wear on the WC tool approximately 4 times and increased the workpiece surface quality compared to the uncoated tool.

Process gas influence on microstructure and mechanical behavior of Inconel 718 fabricated via selective laser melting

The influence of process gas on porosity, microstructure, and mechanical properties of nickel-based superalloy Inconel 718 (IN718) produced via selective laser melting (SLM) was investigated. Density and surface roughness of as-built parts were similar for samples built under nitrogen and argon environments. After hot isostatic pressing (HIP) and precipitation-hardening heat treatments, argon-processed specimen had finer, more uniform grain structures, and increased room-temperature tensile failure strains (> 24%) and yield strengths (> 4%) compared with nitrogen-processed specimen. Elemental analysis showed no variation in composition or nitride precipitate concentration with environment. Larger melt pool structure and heat-treated grain size were produced under argon when laser focus shift was varied away from focal plane, while under nitrogen grain refinement was observed when focus shift is moved in the positive direction. These changes in microstructure are reflected in mechanical properties; the highest strength and ductility is achieved in argon-processed samples at the laser focal plane. To clarify the contribution of thermal conductivity, density, and refractive index of process gas to these observations, samples were built under helium and surface finish and microstructure were evaluated. It was determined that laser interaction with process byproducts is most responsible for differences in as-printed and heat-treated microstructures under each protective environment.

Study of Dry Wear Behavior and Resistance in Samples of a Horizontally Solidified and T6/Heat-Treated Automotive AlSiMg Alloy

To investigate dry wear behavior in an aluminum-based automotive alloy, transient horizontal solidification experiments using a water-cooled directional solidification device have been performed with the Al7Si0.3Mg alloy (wt%). Samples of the as-cast ingot at positions (P) 2, 4, 6, 40, and 80 mm from the cooled interface were subjected to precipitation hardening heat treatment (T6-type). The heat treatment has been applied under the following conditions: solution treatment for 3 h at 520 ± 2 °C, followed by quenching in warm water (70 ± 2 °C), aging for 3 h at 155 ± 2 °C and air-cooling. Dry wear tests were performed on both the as-cast and heat-treated samples. The wear tests were carried out by rotary-fixed ball wear machine means. The analyzed parameters were solidification growth and cooling rates (VL and TR), secondary dendritic spacings (λ2), and wear volume and rate (WV and WR). An interrelation between these parameters has been conducted and experimental mathematical equations have been proposed to characterize the WV and WR dependence on P, VL, TR and λ2. The T6-heat treatment has affected the length of the as-cast dendritic scale, increasing the λ2 values as well as the wear features of the investigated automotive alloy. Finer and coarser dendritic microstructures inherited better wear resistance for the as-cast and heat-treated samples, respectively. An evaluation by occupied area fraction (%IRAF) of interdendritic regions on wear resistance in the as-cast and heat-treated samples has been performed. It has been observed higher and lower IRAF values in the as-cast and heat-treated samples, respectively.

Microstructure and mechanical properties of direct metal laser–sintered 15-5PH steel with different solution annealing heat treatments

15-5PH parts that are fabricated using direct metal laser sintering (DMLS) has shown mechanical properties comparable to conventionally manufactured parts. However, DMLS-fabricated 15-5PH parts have shown high anisotropy in their mechanical properties due to the layering nature of additive manufacturing process. In addition, the fatigue life and strength of DMLS 15-5PH varies significantly between horizontally and vertically fabricated parts and both orientations are inferior to conventionally manufactured parts. Reliability and large variations in performance remain as a barrier from employing 15-5PH parts fabricated using DMLS. Standard heat treatment of 15-5PH is insufficient to eliminate the anisotropy and homogenize the DMLS parts. Modified precipitation hardening heat treatments did not show further improvement in published literature. Therefore, in this paper, we investigate the influence of different solution annealing heat treatments on the microstructure and mechanical properties of 15-5PH steel produced using DMLS. Three different solution annealing heat treatments were investigated: the standard solution heat treatment, the second heat treatment extended the time from 1 to 3 h, the third heat treatment increased the temperature from 1038 to 1200 °C. For each heat treatment, three patches of specimens were fabricated each in one of the three principal orientations X, Y, and Z. In addition, three patches, one of each orientation, were tested in as-built condition. The specimens were tensile tested and their microstructure and fractured surfaces were imaged. It was found that extending the time of the heat treatment improved the homogenization while increasing the temperature of the heat treatment to 1200 °C had detrimental effects, especially on vertically fabricated specimens.

Direct laser deposition as repair technology for a low transformation temperature alloy: Microstructure, residual stress, and properties

Fe-Cr-Ni-Mn-Mo-Nb-Si steel with low transformation temperature was fabricated by direct laser deposition (DLD) and its microstructure, residual stress and properties were investigated. The results demonstrated that the microstructure consisted of martensite laths with a lath spacing in the nano-scale range and a small amount of nano-sized polycrystalline precipitates. There was no grain boundary segregation, and the chemical elements were homogeneously distributed. The tensile strength, yielding strength, elongation and impact energy were 1275 MPa, 1032 MPa, 12% and 57 J respectively. The comprehensive mechanical properties were equivalent with those of the wrought precipitation hardening martensitic stainless steel. There was no Cr-depleted zone at the interface between the matrix and the precipitates as well as the interior at the precipitates, and the corrosion resistance was better than that of FV520B stainless steel. The neutron diffraction (ND) stress analysis results showed that the residual tensile stress level in the cladding layer was relatively low due to the effect of solid phase transition. Consequently, due to the excellent integrated mechanical properties and the residual stress state, there was no need to conduct stress relief and precipitation hardening heat treatment, thus avoiding the influence of heat treatment on the base material properties, and saving resources and funds.

Characterization of SLM-fabricated Inconel 718 after solid solution and precipitation hardening heat treatments

The microstructure and hardness of solid solution heat treated (ST) and precipitation hardened Inconel 718 parts fabricated with selective laser melting are investigated. The temperature range for the ST is between 970 and 1250 °C, while the two-step precipitation hardening was done at 760 and 650 °C, each for 10 h. The result demonstrates the effects of homogenization and consequently the effects of aging on the microstructure and hardness of the samples studied. Complete recrystallization occurred for the specimens ST at and higher than 1180 °C. The grain structures of ST specimens qualitatively appear identical with those specimens ST and aged, implying that aging does not induce noticeable changes in the grain structures. Precipitation hardening generates uniformly distributed good yield of ellipsoidal γ″ precipitates with average size of minor and major axis of 11–17 nm and 48–81 nm, respectively. In addition, smaller quantities of γ′ precipitates with an average size of 24 nm are observed for the aged specimens. Increasing the hold time of ST for a particular temperature leads to coarsening of γ″ precipitates, which have a negative impact on the hardness of the material. After aging, the hardness of the specimens is increased by 32–43% relative to that of the as-printed specimen. The increments in hardness for the specimens ST at and lower than 1100 °C (and aged) are the result of the combined effects of hardening precipitates and strain associated with the lattice defects, such as dislocation networks and subgrain boundaries that remain undissolved. The microstructures of the specimens ST at higher temperatures (e.g., 1250 °C) have attained minimal lattice defects due to completed recrystallization. Hence, the increment in hardness for these specimens after aging is mainly due to the hardening precipitates. Needle-shaped δ phase is also precipitated along/near grain boundaries during solid solution heat treatment at 970 °C. Formation of δ phase can consume a lot of Nb, which otherwise be used for the precipitation of hardening phases.

Effect of heat treatments on microstructural evolution of additively manufactured and wrought 17-4PH stainless steel

Additively manufactured (AM) components usually have nonequilibrium microstructures. Post-built heat treatments are recommended for AM components to achieve homogenous microstructures. In this study, the effects were investigated of conventional solutionizing and precipitation hardening (H-900) heat treatments on the microstructure evolution of 17-4PH AM and wrought components. Microstructural characterization techniques including SEM, TEM and EBSD analysis were used on 17-4PH AM and wrought components to obtain quantitative information about the microstructure and phase evolution during these heat treatments. These microstructural studies demonstrate that 17-4PH AM components can achieve microstructures and hardnesses similar to those of wrought samples by post-built heat treatments.

Fatigue behaviour of Inconel 625 cold spray coatings

ABSTRACTCold spray coatings were produced with Inconel 625 powders sprayed on a heat-treated Inconel 718 substrate. The processing parameters were varied to analyse the microstructural and mechanical variations as a function of cold spray conditions. Cold spray can contribute to improve the fatigue properties of repaired components; the best process conditions, leading to low porosity and high adhesion strength, were employed to produce coatings in notched samples to evaluate the fatigue crack behaviour of the sprayed material. The coatings were heat treated to evaluate the material microstructural evolution and mechanical properties. The crack initiation and growth behaviour of the coatings was studied also for the solution and precipitation hardening heat treatment condition to compare the fatigue behaviour with that belonging to the as sprayed one. It was demonstrated that the heat treatment has a beneficial effect on fatigue cracks retardation.

Effect of Heat Treatment on Slurry Erosive Wear Behaviour of Al 6061 Based Composites

ABSTRACT In the present investigation, Titanium di oxide (TiO2) reinforced Al 6061 compositesIn the present investigation, Titanium di oxide (TiO2) reinforced Al 6061 compositesfabricated using liquid metallurgy route with varying proportions by weight viz 4, 6, 8 and 10percentage were subjected to precipitation hardening heat treatment. The performance of heattreated Al 6061 based Titanium di oxide composites in slurry erosive environment was examined.The slurry consists of equiaxed sand particles of size approximately 600 μm in 3.5%NaCl solution.The slurry erosive wear studies on heat treated Al 6061 alloy and Al 6061-TiO2 composites werecarried out at under different test conditions. It was observed that with an increase in aging durationfor all the quenching medias and for all the given test conditions there is a reduction in slurryerosive wear rate of both the base alloy and the composites, however ice as quenching media hasa profound effect on the slurry erosive wear rate of both the base alloy and the composites studied.

Effect of the T6 Heat Treatment on Microhardness of a Directionally Solidified Aluminum-Based 319 Alloy

Aluminum alloys of the ANSI series 319 present Si and Cu as the main alloying elements and the mechanical strength of these alloys can be improved by the precipitation of the metastable Al2Cu phase during the ageing heat treatment. In this paper, the Al-5.5wt.%Si-3wt.%Cu alloy was elaborated and solidified in a water-cooled horizontal directional solidification device. The as-cast ingot was subjected to the precipitation hardening heat treatment (T6 heat treatment), which consisted of: solution for 5 h at 490°C±2°C, followed by quenching in water at 60°C±2°C and ageing for 3 h at 155°C±2°C, and cooling-air. Secondary dendrite arm spacing (λ2) measurements were carried out before and after T6 heat treatment. The mechanical strength of the alloy was investigated by the microhardness test. It has been found that the heat treatment did not influence the λ2 values, however, highest HV values have been observed for the heat-treated samples.

Effect of precipitation hardening heat treatment on mechanical and microstructure features of dissimilar friction stir welded AA2024-T6 and AA6061-T6 alloys

The friction stir welding of AA2024-T6 to AA6061-T6 plates with a 4mm thickness has been studied at constant traverse and rotational speeds of 1000rpm and 100mm/min, respectively. The position of alloys and the effects of precipitation hardening heat treatment in retreating and advancing side in the friction stir welding were analyzed. The tool with taper threaded pin was used for welding. Macro and microstructural analysis were investigated by using Optical and Field Emission-Scanning Electron Microscopes (FE-SEM) to check out the welded joints. Micro-hardness and Tensile tests were also done to study mechanical attributes of the joints. Microstructural analysis revealed some grain coarsening in the weld zones and base metals after heat treatment. The results also showed that mixing between the two alloys and their tensile strength improved when AA6061 alloy was placed on the advancing part. Furthermore, the ultimate tensile strength of the heat treated welds was higher than non-heat treated welds which can be attributed to increasing of strength and hardness of weld zones, especially HAZ. Besides, the fracture area of the welded joints shifted from the HAZ of AA6061 to the SZ which confirms significant role of precipitation hardening heat treatment on the mechanical effects of the welded joints. In the SEM images of the fracture surface, precipitated Mg2Si particles in HAZ were observed.

Anodizing and Corrosion Resistance of Aluminum AA7050 Friction Stir Welds

Friction Stir Welding (FSW) is a solid-state joining technique with various advantages when compared to other welding methods, being therefore a very important and promising process for the aerospace industry. This technique is particularly well suited for high-strength aluminum alloys based on the Al-Cu-Mg and Al-Zn-Cu systems, which undergo well defined precipitation hardening heat treatments and suffer loss of mechanical properties and occurrence of defects if welded by methods that involve fusion. The alloying elements and the heat treatments applied to these alloys also make them highly susceptible to localized corrosion, and thus a coating process such as anodizing becomes necessary. Considering that the existence of second phase particles and flaws in the substrate can affect the quality of the oxide coating obtained by anodizing, the influence of FSW on a subsequent anodizing process must be assessed. In this work, we studied the impact of the microstructure created by FSW on the thickness, structure, and corrosion resistance of anodic oxide coatings. An AA7050 profile was friction stir welded to an AA2024 sheet, in order to simulate the assembly of airplane stringers and skin. During FSW, the AA7050 side was facing the welding tool, receiving intense heat and deformation. As a first approach this surface was selected for anodizing, for it is the side that is most modified. The weld was characterized by optical and scanning electron microscopy, and 3 different zones were distinguished: heat affected zone, thermomecanically affected zone (TMAZ), and the nugget (the center, where recrystallization occurs). Vickers hardness measurements revealed a lower hardness at the frontier between thermomecanically affected zone and heat affected zone, possibly due to dissolution of precipitates. The welds were galvanostatically anodized in sulfuric electrolyte. Scanning electron micrographs showed that, on the TMAZ, the anodic oxide is thicker than on the base material and the metal/oxide interface is flat. On the nugget zone, however, the anodic oxide is thinner and more defective, and the metal/oxide interface is rougher. There appears to be a relation between the presence of hardening precipitates (MgZn2 was found mostly in the nugget) and thinner anodic films. Accordingly, TMAZ was the zone with the thickest anodic oxide films, and the lowest hardness. Defects related to the dissolution of Al7Cu2Fe precipitates were found in the oxide layers on all zones and inferences about how they affect anodization kinetics are drawn. The Scanning Vibrating Electrode Technique (SVET) was used to test the corrosion resistance of anodic oxide layers in chloride media. The samples were scanned simultaneously to anodic polarization at a potential higher than the AA7050 alloy’s pitting potential. Results showed that pitting happened preferentially on the nugget zone and its frontier with the TMAZ. Finally, pit current transients were calculated from SVET maps, allowing visualization of the evolution of pits. Figure 1

Effect of Cryogenic Treatment on the Mechanical Properties of 18Ni-300 Grade Maraging Steel Built Using the Direct Metal Laser Sintering (DMLS) Technology

Maraging steels belong to the class of steels that are found to have a unique combination of ultra-high strength and good fracture toughness, due to which they find uses in critical applications such as aircraft forgings, pressure vessels, missile casings, hydraulic hoses etc. Several studies on the effect of cryogenic treatment on various grades of Tool steels & Maraging steels have shown significant improvements in mechanical properties and dimensional stability.DMLS (Direct Metal Laser Sintering), an additive manufacturing technology, is increasingly becoming popular to build intricate high quality functional parts & rapid prototypes. DMLS technology uses a high intensity laser to build components layer by layer, directly from CAD data without the need for tooling. It is possible to build internal features and passages that are not possible in conventional manufacturing routes. Maraging Steel is used extensively to build functional parts by DMLS process especially for Tool and Die applications. However, very few findings have been reported on the effect of cryogenic treatment on the mechanical properties of Maraging steel built through this route. In this study, effect of cryogenic treatment on Maraging Steel grade 300 built by DMLS process is discussed. Test specimens were built in horizontal and vertical directions to see the effect of build direction on the properties. Half the specimens were given standard DMLS precipitation hardening heat treatment and the rest were given cryogenic treatment in addition to routine thermal treatment. Mechanical properties such as - tensile, impact properties , hardness, & density between the two sets of treatments are reported and discussed. Metallurgical structures are compared and findings are also reported.

Evolution of the microstructure of a 15-5PH martensitic stainless steel during precipitation hardening heat treatment

The mechanical properties of precipitation-hardened stainless steels rely on a complex multi-scale microstructure developed during a sequence of quenching after austenitization, followed by a precipitation heat treatment. Important features of the resulting microstructure include the microstructure of martensite, retained and reverted austenite, nanoscale precipitation and the homogeneity of the Cr concentration. In this paper, the microstructure of a Cu-bearing 15-5PH steel is thoroughly characterized along the precipitation heat treatment, using a combination of transmission electron microscopy with phase and orientation mapping, atom probe tomography, in-situ small-angle X-ray scattering and X-ray diffraction. The fraction of austenite is observed to increase during the ageing treatment, together with the precipitation of the Cu precipitates, which present a core-shell structure with a shell enriched in Ni, Mn and Si. After heat treatment, the Cr concentration is found to be slightly inhomogeneous in the matrix, with some segregations at the dislocations.